1. The Field of the Invention
This invention relates to photographic products and processes and particularly to diffusion transfer photographic products and processes.
2. Description of the Prior Art
Diffusion transfer photographic products and processes are known to the art and details relating to them can be found in U.S. Pat. Nos. 2,983,606; 3,415,644; 3,415,645; 3,415,646; 3,473,925; 3,482,972; 3,551,406; 3,573,042; 3,573,043; 3,573,044; 3,576,625; 3,576,626; 3,578,540, 3,569,333; 3,579,333; 3,594,164; 3,594,165; 3,597,200; 3,647,437; 3,672,486; 3,672,890; 3,705,184; 3,752,836; 3,857,865 and British Pat. No. 1,330,524.
Essentially, diffusion transfer photographic products and processes involve film units having a photosensitive system including at least one silver halide layer usually integrated with an image-providing material. After photoexposure, the photosensitive system is developed to establish an imagewise distribution of a diffusible image-providing material, at least a portion of which is transferred by diffusion to an image-receiving element having a layer capable of mordanting or otherwise fixing the transferred image-providing material. In some diffusion transfer products, the transfer image is viewed by reflection after separation of the image-receiving element from the photosensitive system. In other products, however, such separation is not required and, instead, the transfer image in the image-receiving layer is viewed against a reflecting background usually provided by a dispersion of white, light-reflecting pigment--such as titanium dioxide.
Diffusion transfer photographic products providing a dye image viewable against a reflecting background without separation are oftentimes referred to in the art as "integral negative-positive film units" and such units are of two general types. Integral negative-positive film units of a first type are described, for example, in the above-noted U.S. Pat. No. 3,415,644. Such film units include a photosensitive system and associated dye image-providing material carried on an opaque support, an image-receiving layer carried on a transparent support and means for distributing a processing composition between the elements of the film unit. Photoexposure is made through the transparent support and image-receiving layer and a processing composition which includes a reflecting pigment is distributed between the image-receiving and photosensitive components. After distribution of the processing composition and before processing is complete, the film unit can be--and usually is--transported into conditions of ambient light to permit in-light processing.
Accordingly, in integral negative-positive film units of this type, the layer provided by distributing the reflecting pigment must be capable of performing certain functions. For example, the distributed reflecting layer must be able to provide at least partial protection against further exposure of the photoexposed element if the film unit is transported into ambient light conditions before processing is completed. At the same time, however, the layer must be sufficiently permeable to permit effective transfer of image dyes from the photoexposed photosensitive layer or layers to the image-receiving layer. Moreover, after transfer, the layer must provide a reflecting background of suitable efficiency for viewing the dye image transferred to the image-receiving layer. Also, in film units of this type, the reflecting layer should effectively mask the photoexposed photosensitive layer or layers.
Integral negative-positive film units of a second type, as described, for example, in U.S. Pat. No. 3,594,165, include a transparent support, carrying the appropriate photosensitive layers and associated image dye-providing materials, a permeable opaque layer, a permeable light-reflecting pigment-containing layer, an image-receiving layer viewable through a transparent support against the light-reflecting layer, and means for distributing a processing composition between the photosensitive layer and a transparent cover or spreader sheet. Additionally, integral negative-positive film units of this second type include an opaque processing composition which is distributed after photoexposure to provide a second opaque layer which can prevent additional exposure of the photosensitive element.
In film units of this second type, exposure is made through the transparent cover sheet. After distribution of the processing composition and installation of the second opaque layer, this type of film unit can also be transported into light before processing is complete. Accordingly, in film units of this second type, the light-reflecting pigment-containing layer may also perform the functions of providing at least partial protection for the photoexposed element until processing is complete but, again, this layer must permit effective transfer of image dyes to the image-receiving layer. Also, like the film units of the "first type", the layer must provide a suitable reflecting background for viewing the dye image transferred to the image-receiving layer. Moreover, effective masking of the photoexposed photosensitive layer must also be achieved for film units of this "second type".
In many known integral negative-positive film units, temporary opacification systems have been used in combination with light-reflecting layers and light-reflecting layer materials. These temporary opacification systems are desiged to cooperate with the reflecting layer and/or reflecting layer materials to provide sufficient opacity to prevent further exposure of the film unit through the reflecting layer during processing of the film unit in light.
U.S. Pat. No. 3,647,437, for example, describes a temporary opacification system that has been used extensively in commercial integral negative-positive film units of the first type, e.g., film units of the type described in U.S. Pat. No. 3,415,644. That temporary opacification system essentially involves a pH-sensitive agent which can absorb light at one pH but is rendered substantially non-light absorbing at another pH. As disclosed in U.S. Pat. No. 3,647,437, the optical filter agent is usually dispersed in the film unit's processing composition together with a light-reflecting pigment. In turn, the processing composition is integrated with elements of the film unit so that the composition can be distributed between the photoexposed photosensitive layer or layers and the image-receiving layer. Accordingly, after distribution of the processing composition, an opaque layer comprising the reflecting pigment and optical filter agent is provided and the opaque layer covers a major surface of the photoexposed layer. This light-absorbing filter agent cooperates with the reflecting pigment to provide a reflecting layer having a degree of opacity sufficient to prevent photoexposure through the layer. As development and transfer of dye image material proceeds, the pH of the film unit changes so that the light-absorbing capability of the pH-sensitive optical filter agent is reduced until it becomes substantially non-light absorbing and its opacity-providing function is diminished. When processing is complete, the reflecting layer--now comprising the reflecting pigment and decolorized optical filter agent--provides a white background for viewing the dye image and for masking the developed photoexposed layers.
Additional details relating to pH-sensitive optical filter agents useful in diffusion transfer photographic products and processes can be found in U.S. Pat. Nos. 3,702,244 and 3,702,245 among others.